Burning the World in Unholy Fire
by CP Nightshade
Summary: "You have a dark heart in you, Valentine's daughter." Those were the words Sebastian had told her what seemed like an eternity ago. Now, in Edom, she feels the very truth of those words in her very soul. When darkness takes the daughter of Angels, what light is left to shine upon the world? Dark Clary/Sebastian. CoHF spoilers.
1. Chapter 1

**Okay, I know I have another fanfic kinda just sitting there right now. But I just read the City of Heavenly Fire, and this idea crossed my mind fairly early in the book. So when it gave me the opportunity to actually happen at a reasonable time, well it happened. There are spoilers in her the CoHF, as well as incest. Personally, I'm no huge fan of it but this idea grew inside my head and now here it is. Oh, and this is my first MI fanfic, so tell me how I do.**

She saw Jace swallow. He dropped the bracelet into Sebastian's open palm. "Clary is yours," he said, and stepped back.

Sebastian snapped his fingers. "You heard her," he said. "All of you. Kneel to your queen."

Clary found herself wanting to protest, to cry out, to tell them not to kneel. She forced herself into stillness, silence. She watched as the Endarkened began to kneel, one by one, their heads bowed; the last to kneel was Amatis, and she did not bow her head. Luke was staring at his sister, his face flayed open. It was the first time he had seen her like this, Clary realized, though he had been told of it.

Amatis turned and looked over her shoulder at the Shadowhunters. Her gaze caught on her brother's for just a moment; her lip curled. It was a vicious look. "Do it," she said. "Kneel, or I will kill you."

Magnus knelt first. Clary would've never guessed that. Magnus was so proud, but then it was a pride that transcended the emptiness of gestures. Despite her earlier resolve to not want her friends to kneel down, she kept hearing Sebastian's voice in her head, repeating the same saying over and over. _You have a dark heart in you, daughter of Valentine._ She felt her will, which she hoped had foundations deep enough to withstand anything Sebastian has planned begin to shake a falter. She felt the darkness, felt it seep out from within her very core and she felt its icy cold tendrils grip her heart like a vice.

She expected it to be unpleasant, to be painful or heart wrenching, but Clary did not expect the darkness to feel so… alluring. She was surprised, but in the good way. She felt it seep into her soul; the very thing she had hoped to never feel. Though now that she had felt it, if only for a brief time…

She wanted _more_.

And she got her wish as Alec soon followed Magnus, kneeling before Clary on her throne of melted gold and ivory bone. Isabelle followed soon after, then Simon, then Luke, drawing Clary's mother beside him. And lastly Jace, his blond head, now dulled in Clary's sight. His brightness, the light that was increased tenfold by the heavenly fire the used to rage within him, and now that Clary had siphoned the fire into Heosphorus by the work of Ithuriel's rune, he seemed to be even more ashen. She had originally planned to use the holy fire on Sebastian, but now she was starting to like the idea of ruling from her pale throne, her brother at her side.

Once they were all bowed before her, Sebastian moved towards the platform taking the steps two at a time towards Clary, and reached up to take her hands; she let him draw her, until she stood in front of him. He was still holding her. His hands felt like bracelets of fire around her wrists, spreading a tingling sensation throughout her body. "You accept it," he said. "You accept your choice?"

"I accept it, she said, looking at him with absolute directness. "I wholeheartedly accept." By now, a small smile had crept to her face of its own accord. She could feel the shadows inside her reveling in joy, and the cool pleasure that it shared with her only made her grin wider.

Sebastian's onyx eyes locked with hers. "Then kiss me," he said. "Kiss me like you love me."

Her original thought when Jace and her had created this plan and brought this very action up was that she would be disgusted. She believed she would recoil, be disgusted by the fact that she might have to kiss her brother. Now, she didn't see Sebastian as just her brother. She saw him as a king, as a conqueror. She could see him leading battles and slaughtering his enemies and bathing in their blood. The darkness in her wanted to join, and she could not resist the pull it had on her. So she leaned in, rising up to the tips of her toes, and kissed Sebastian.

When their lips met, she could almost hear the shadows in her soul cry out in joy. The chill it brought to her body made her shiver in pleasure. She wrapped her arms around his neck and deepened the kiss. Clary opened her mouth and swirled her tongue across Sebastian's lips, to which he eagerly opened his mouth and their tongues met. Clary would've of continued, but she heard Jace yell out her name, "Clary!"

She drew back from Sebastian with a look of annoyance on her face. She looked into her brother's eyes and smiled slightly, before giving a teasing wink and whispering to him softly, "Later." His face broke into an enormous grin. She unwrapped her hands from around his neck before she turned and looked down at Jace who was now standing. She gave him a scathing look before addressing him evenly, "Jonathon Herondale."

Jace recoiled at her tone of voice. Her normally soft yet firm voice was replaced by an emotionless, cold one, eerily similar to tone Sabastian used. He looked at her, noticing how the bright and lively demeanor she once had was replaced by a shadow, emotionless and icy. "The plan," he said. "What are you doing?" His face was so shattered, so weak. Clary felt the darkness stir, obviously aware at the person trying to remind her of the plan to kill Sebastian, her king.

Clary cocked her head to one side, staring at him as if she was dissecting him to find out what was wrong her. "I suppose those who do not share the Morgenstern blood cannot feel it," she began. "You feel the angel's blood thrumming in your veins, leading you to do good in the world."

Clary began to descend from the dais, and she stood inside the circle of dark runes. The windows still stood, and Clary looked at the shimmering green beauty of Idris and Alicante with disgust. The shadows that swirled in her soul didn't like the look of such untainted lands, and it recoiled even at the sight of them making Clary feel slightly clammy just staring at them. She diverted her attention back to Jace. "You have the blood of Raziel, a heavenly angel through and through," she said, and then turned and looked at Sebastian. "My brother and I, we have the blood of Lucifer, the morning star. We were both destined to fall, sooner or later."

Jace looked at her, confused as to why Clary was acting this way. Concern showed in his eyes, and with a further look it showed in the eyes of those around him. She thought, and hid a snigger, that if her "friends" thought she needed help, that they didn't know her well enough to call her "friend" at all. Clary stared into Jace's golden eyes, her emerald ones darker than he'd ever seen. "You can't believe that," Jace said. "You can't, it's just not you."

Clary snorted in a very un-lady like fashion. "And who are you to dictate what I can believe?"

Jace as at a loss for words, but his confrontation spurred Simon into stepping forwards. "You can't Clary. You were the greatest of all Nephalem, your powers and your increased angel blood made you the brightest of all stars."

At this, Clary just gave an agitated sigh. "You need to seriously work on your listening skills," she said as she put the heel of her hand against her forehead. "Lucifer was the brightest of all the angels in heaven, and he fell. So as I said earlier, it goes to point that those with the blood of the morning star fall from heaven's grace."

This time, it was Jocelyn who spoke up. "And you're okay with that!" she yelled at Clary. Jocelyn started to move forwards, but Amatis and the other Endarkened had risen and moved to protect their queen. They moved to restrain Jocelyn, but Clary simply raised her hand and they formed a loose semicircle before her.

Clary gave her mother a cool, collected looked. "Dear mother," she said with a voice of venom. "How does it feel to sire the King and Queen of Edom? I doubt the Shadowhunters would welcome you with open arms, but then again neither would we." Jocelyn recoiled away from her daughter. "You are the birthmother to two of the most powerful beings that can or will wield demonic power, which leaves the question: what does that make you?" Clary gave her mother a cruel smirk, and she felt the darkness thrum with glee.

Jocelyn began to cry, and Luke came up to her and hugged her tightly. Jocelyn spoke, tears and sobs choking her speech, "You are no longer any daughter of mine."

At this Clary just raised an eyebrow and her lips quirked even more. "How fitting," she replied, her voice cutting like a blade. "Because you are no longer any mother of mine." At her reply, Jocelyn cried harder into Luke's shoulder. Clary cast a look around at the company before her, noticing them all glaring at her with hatred except for Jace, who merely glared at Sebastian upon his throne instead.

Clary moved up so she was right behind Amatis. "See that our guests are moved through the window," she told the King's, and now her, lieutenant. "I wish to spend time with my King and have no time to spare for such a rebellious and ignorant bunch."

Amatis and the other Endarkened moved forwards to usher the werewolf, Nephalem, Daylighter, and warlock towards the window that lead to Idris. Clary turned around to ascend back to her throne next to Sebastian, but turned around when the sounds of combat came from below. Jace had gotten past the Endarkened somehow and was making his way towards Clary. Clary looked at his gaze, and saw his eyes were locked on blade at her hilt. Knowing what he planned to do, she snarled and drew Heosphorus from its scabbard.

The blade was at the throat of Jace in a second, golden flames licking along the stars of the Morgenstern blade. She narrowed his eyes at the Herondale boy as the Endarkened surrounded the both of them. They hissed at Jace, and pulled him back savagely so that he was on his knees before her. "Now what," she began, "did you hope to gain from doing that?"

Jace just continued to look at her with betrayal in his eyes. Finally, after he saw the Clary's attitude was unchanged he answered. "The plan," he said. "I was going to finish the plan and take Heosphorus and stab it through his chest." He pointed at Sebastian who was now standing at the edge of the platform, fists balled as he glowered at Jace.

Clary moved forwards as to deliver a blow, but she just crouched in front of the Herondale. "If you so much as make another move for the blade or against Sebastian, I will kill you." She gave him a once over. "And I'll enjoy every long second of it." She addressed the Endarkened, "Get him out of here. Now!"

The Endarkened ones moved to finally take him out with the others. Just before the last one was thrown back into Idris, Clary heard Jace ask, "Why?"

Clary gave a low chuckle, and despite Jace not being able to hear she answered him. "Oh Jonathan, you should've realized by now. The brightest of lights always cast the darkest of shadows." She turned away from the window and gave Sebastian a smile as he descended to finish off the circle to close off this world from the other. When he bent down over the rune circle, he traced one last rune into the ground.

At first, the windows seemed to crack and fracture. Spider webs chased each other to and fro along the image of Idris and other worlds. After that, they fell like a waterfall: slow at first, tinkling ever so slightly as the hit the ground before roaring and hitting the ground in a cascade of melodically ringing pieces.

Clary moved over to Sebastian so that when he straightened up and turned around she would be right there. When he did straighten, Clary put her arms around his neck once again and rose to her tip toes and kissed him quickly. Sebastian leaned into at first, but then pulled back for a second. He turned his head to the remaining Endarkened and spoke, his voice carrying its normal high authority, "Leave us."

When the Endarkened had left, Sebastian turned back to Clary and slammed his lips ferociously into hers, eliciting a small gasp from the red head. Sebastian's tongue met Clary's and the wrestled for dominance. Clary felt herself wrap her legs around his waist and his hands move down towards her hips. She felt the darkness in her trill again, sending another shiver of pleasure through her body. She drew back a little and gasped when Sebastian started to massage her rear with his strong hands. Her brother moved to kiss her neck, sending ecstasy coursing through her cells.

Clary was about to suggest they take this somewhere more suitable, but she didn't get the chance as a rich, velvety laugh echoed off the walls. The pair pulled apart and looked down at the base of the dais to see a tall woman with hair the color of ebony and eyes like molten obsidian. The woman's skin was pale under the deep black dress she wore. The dress itself went down to her ankles and draped itself over the woman's shoulder. Clary could only compare the woman to a celebrity or super model, and even then it barely held a candle to the woman's beauty.

Clary was confused for a small moment, before she recognized the woman. "Mother!" Sebastian said, voice sounding happy and carefree which was incredibly new to Clary. Sebastian took a step back from Clary, giving them acceptable distance though he still held Clary's hand in his own.

"My dear son," Lilith said to Sebastian, approaching him with arms wide open. Sebastian let go of Clary's hand and embraced Lilith. Lilith moved back and put her hands on his shoulders in a surprisingly motherly gesture. "Are you alright? Did everything go to plan?"

Clary found the concern in Lilith's voice odd, considering that all she knew about her was that she was the mother to almost every demon, though Sebastian was unperturbed. "Everything went fine, but not exactly according to plan," he told Lilith, a grin breaking across his face. "It went better than any of us could have foreseen."

Lilith gave him a questioning glance, raising one of her dark eyebrows. "Oh?" she began, a smile forming across her perfect features. "Please do share; I love it when everything works out."

At this, Sebastian stepped back from his mother and grasped Clary's hand again. "It would seem, after an interesting turn of events, that I did not need to persuade Clarissa after all," Sebastian looked at her and his eyes held such pride, that Clary felt overwhelmingly giddy. "She came of her own free will, and even disowned Jocelyn right here. Even with all the amazing things I have seen, Clarissa managed to strike me with awe once again." Sebastian bent over and gave her a quick peck on the lips, making heat rise up and flush her cheeks a light red.

Clary, feeling the need to supply some sort of input, spoke up, her voice sounding surprisingly calm, "It was nothing special, just the bald truth." At this Sebastian just gave a booming laugh.

"Just the bald truth?" he asked, his voice carrying a playful edge that once again surprised Clary. "What was it you said? About following in Lucifer's footsteps?"

Clary looked at her feet, feebly attempting to hide the heat rising to her cheeks. "I said that the Morgensterns have the blood of Lucifer in our veins, so it is only fitting that we fall as he did." Clary looked up again, seeing Sebastian's onyx eyes so lively. It was strange, but she could still see the coldness that was waiting, lurking just beneath the surface. It was that coldness that the darkness in her desired, but she could not deny that she enjoyed this side of Sebastian as well.

Clary felt a pair of delicate hands grasp her shoulders and she looked to see Lilith looking at her with what seemed to be actual respect. "Oh my," she said, her voice sounding as soft as silk. "I do believe you were right Sebastian. Clarissa here will make an excellent queen."

Lilith than took a step back, looking over the both of them as a pair. She grinned, and then beckoned them to follow. "Come now," she began as she turned to walk out of the Garde. "We have much to do for our new queen."

Clarissa and Sebastian followed behind Lilith, hands intertwined. As they exited, Sebastian leaned over and whispered into Clary's ear, "Later?"

Clary couldn't help to wolfish grin that spread across her face. She leaned over towards his ear and whispered back, "Later." And the darkness in her soul chorused in agreement.

**Thank you all who read this, and please leave a review or send in a PM. Criticism is welcome, but flames aren't.**

**CP out**


	2. Chapter 2: Interlude

WARNING: Chapter contains signs of depression and displays of animal cruelty.

Disclaimer: I do not own the Mortal Instruments, as it belongs to Cassandra Clare.

_Interlude_

They say time heals all wounds, but Jace can attest that is not true. It has been three years since they left Edom under armed escort, and every second tortured his shredded soul. Clary's betrayal felt as if Luke and Simon had decided to have a feast on him for eternity, and that was only the physical pain. The mental pain scales beyond any word made in any language.

After they all left, they appeared on a torn up plain not far away from Alicante. The Glass City, they could tell, was damaged, but it was not broken and could still be repaired. They could see the Nephalem raising a banner of victory from the few still standing Demon Towers, but to their group, no victory was worth the cost that had been payed.

All of them had seen Clary, the darkness that had corrupted her. And everyone of them knew it was Jace who was struck the hardest. True Jocelyn may be heartbroken, but she loved Clary as a mother does a daughter, while infinite, it still did not encompass the sheer magnitude of emotion Jace felt towards Clary. Now, after all they had worked for, all they had fought and suffered through, they lost what seemed to be their hearts, the light that shines hope upon their world.

After three years, Jocelyn was improving but still suffered, mostly at night. Luke was by her side faithfully through all the years, but Jace was alone in his torment. Alec and Isabelle did their best to help him, but the only time Jace was anything like his old self was when he was Demon Hunting. Though the Nephalem noticed the scarcity of demons after the war with the Morgenstern family. It was as if the demons no longer _wanted_ to take over Earth. Either that or they were finally becoming extinct, but from what they knew they couldn't actually kill them, just send them back to Edom.

But little of that seemed to matter now at the New York Institute, where the two Lightwood children watched there adopted brother with dreary concern, wishing they had some way to alleviate his pain. Whereas the Herondale simply kept socializing to a minimum, and focused more and more of himself to his fighting, however little he actually got to use it nowadays.

Isabella watched her surrogate brother with a deep sadness in her dark eyes, which were clouded with worry and unshed tears. She watched with Alec as Jace slipped away day by day, still too damaged from the event that conspired in Edom to even begin a healing process. She turned toward Alec, and beckoned him out the door and into the hall. Church passed by with his usual careless gate, seemingly oblivious to the constant air of depression inside the Institute.

"Come on Alec," Izzy said softly, beginning to walk toward their rooms. "There isn't anything left to do."

Normally Alec would argue, persist on finding something to do for Jace, but years of his parabatai throwing himself into training and disregarding everything else had begun to deter him. So he followed his sister silently, a grim look upon his face as he left Jace to his training, alone.

(^')Linebreak('^)

_At last it has begun,_

_as fate is done._

_For now we sing,_

'_till sword 'gain ring._

_For those who fell,_

_can still rise from hell._

_As light is forsaken,_

_foul darkness awaken._

_Now angels sing,_

_as swords do ring._

_The world is torn,_

_to be a soul, reborn._

_At last has begun,_

_and now fate is done._

_-Excerpt from the New Script of Edom Book 2, Shadow's Rise: 12-16, dated December 12, Year 7 of the Endarkened._

The sharp sound of heavy leather folding over itself resonated itself throughout the dark room with a _thud_. The crinkle of dry vellum accompanied by the aroma of old animal skin permeated throughout the room. A few candles lit the room, illuminating an ornate bookcase carved from the black wood of a corrupted elder tree. Books lined the majority of the shelves, the rest contained sketches, varying from a drawings of an obvious lover, to the gruesome disembowelment of a multitude of creatures.

In the middle of the room was a desk, carved from similar black wood, but this was from the Cypress instead of an Elder. Sitting at the desk, carefully moving drying sand into a small bowl before putting a stopper into the little red bottle of ink, was a young woman. She wore simple black blouse and pants, which revealed the intricated lines of runes that ran across her skin in an elegant dance, ending just before her neck and going slightly past her forearms. Some of the symbols shined in different colors, some a red so dark, it barely looked different. And then some were gold and silver, faded into her skin so that they no longer possessed any sheen, but still held power. Her wine colored hair was pulled up into a simple ponytail, with a few loose strands left to frame her flawless face. Her eyes, which held dashes of emerald, were primarily a deep, ebony color. Her face was pale; her cheekbones angular. Her slim eyebrows were seated delicately above her eyes.

The woman reached over and placed the inkwell down, picking up a simple black stele instead. Next, the woman stood. She picked up a candle in her hand and moved over to the corner, where two small, glass cases were. In one, was a mouse, and in the other was a small cardinal. The woman carefully placed down the candle and grabbed the mouse, who didn't squirm or make even a squeak. The woman the carefully began the trace a rune along the mouse's side. The rune flowed as one line in a wave towards a vortex drawn into the mouse. Carefully, the woman placed the mouse back in it's cage.

She then proceeded to retrieve the small cardinal, who, unlike the mouse, did it's best to get away from her. The girl simply grabbed it swiftly, capturing it in her deceptively strong fingers. She then ruthlessly used her free hands to break both of it's wings, to which it started to scream, before it was swiftly silenced when she applied pressure to its lower spine, paralyzing it without killing it. Last, she placed it in the same container as the mouse, where it whimpered pathetically.

The woman the watched with amusement as the mouse approached the bird, an appreciated hunger in its eyes. It pounced on the bird, ripping it's throat with ease, but that is not what the girl truly cared about. While the killing did amuse her slightly, she wanted to see what happened after.

Her eyes lit up at the same time the rune on the mouse's side did, and she watched with ever increasing glee as the mouse hunched over in pain. She also took note of the dead bird, which was turning black, as if being covered in ink. The bird then slowly began to dissolve into black sand, and then continued to move towards the convulsing mouse where it covered it. A few moments later the ball of sand began to expand, revealing a the mouse… only with a few small changes.

First off, the mouse had grown wings out of its back. Second, its claws had grown slightly more curved and sharp. Lastly, the mouse's eyes seemed more aware, more intelligent. The woman ecstatically dashed over to her bookshelf, grabbing a small, leather bound book from the shelf. Swiftly, she had sat down at the desk, opened the book and inkwell, grabbed the quill, and began writing down her observations.

_Subject has shown the rune's true power. Not only did the subject survive, it utilized the _traicio _rune without any damaging symptoms. Observations will be made on daily basis to track any side effect the rune may have._

_-C.A.M._

She quickly set that aside to dry, meanwhile grabbing another paper to begin to write again. She quickly pulled out a piece of parchment and began writing again, this time, a letter. When she finished, she applied a trace amount of the drying sand to pick up excess ink and avoid smudges. Finally, she folded the letter and placed it into an envelope. She then turned it over, and quickly wrote in a small, red flourish: _Lady Lilith_. She proceeded in then turning it over, grabbing a heavy metal stamper, and pressing the thick wax seal over the envelope, sealing it. She then went to a near invisible spot in the wall and slid it down a chute.

Smiling, the woman then sat in her desk, placed her feet upon the desk, and muttered to herself, "Well done Clarissa, well done indeed."


End file.
